Organic light emitting display (OLED) has been deemed as a newly emerging technology of the next generation of flat-panel displays because of such excellent characteristics as self-emission, no need of backlight source, high contrast, small thickness, wide viewing angle, fast response time, possibility of using in a flexible substrate, wide operating temperature range, simple structure and manufacturing processes etc.
An OLED display panel comprises a substrate, a (Indium Tin Oxide) (ITO) anode, a light emitting layer and a cathode etc., and its light emitting principle is that electrons and holes are recombined within the light emitting layer to fall into a lower energy band under the effect of a voltage, and emit photons which have the same energy as the energy gap, and its wavelength (emission color) depends on the magnitude of the energy gap of the light emitting layer. Therein, the light emitting layer is generally manufactured by an inkjet printing technology in which a pixel defining layer (PDL) is required to be made on the substrate in advance to define the pixel areas into which ink droplets are accurately sprayed. However, because the PDL is generally formed with an organic material film by using a photolithography process, a large exposure amount is required for the purpose of no photoresist residues, thereby resulting in a large Critical Dimension bias (around 2.0 μm). Moreover, it is further required that the organic material film is cured after form formation and the curing process may cause the organic material to contract such that the critical dimension bias further increases.
The above-mentioned Critical Dimension (referred to herein as “CD”) is a specialized line pattern which is especially designed to indicate the width of feature lines of an integrated circuit for the purpose of evaluating and controlling the pattern processing precision of the integrated circuit photomask manufacturing and photolithography process. The critical dimension bias is the “After etch inspection CD” minus “the After develop inspection CD”, and is used for characterizing the etching amount and the etching uniformity and therefore is a very important data parameter during production which may be simply understood as the difference between the etching design value and the etching actual value, i.e., the etching bias.